Accurate photon echo timing by optical freezing of exciton dephasing and rephasing in quantum dots

Semiconductor quantum dots are excellent candidates for ultrafast coherent manipulation of qubits by laser pulses on picosecond timescales or even faster. In inhomogeneous ensembles a macroscopic optical polarization decays rapidly due to dephasing, which, however, is reversible in photon echoes carrying complete information about the coherent ensemble dynamics. Control of the echo emission time is mandatory for applications. Here, we propose a concept to reach this goal. In a two-pulse photon echo sequence, we apply an additional resonant control pulse with multiple of 2π area. Depending on its arrival time, the control slows down dephasing or rephasing of the exciton ensemble during its action. We demonstrate for self-assembled (In,Ga)As quantum dots that the photon echo emission time can be retarded or advanced by up to 5 ps relative to its nominal appearance time without control. This versatile protocol may be used to obtain significantly longer temporal shifts for suitably tailored control pulses.

THE NANOCRYSTALS SIZE ESTIMATION USING RAMAN SPECTROSCOPY IN A-SIOX:H FILMS AFTER CRYSTALLIZATION OF SILICON NANOCLUSTERS

The a-SiOx thin films with silicon nanoclusters are currently being actively studied by various laboratories due to the possibility of efficient control of their optical properties, both at the stage of formation and using technological treatments. The presence of excess silicon in such films leads to the growth of nanocrystals during high-temperature annealing, which affects the optical properties of SiOx films, including photoluminescence. Therefore, in this work, we studied the formation of silicon nanocrystals in a-SiOx films during Pulse Photon Annealing (PPA). X-ray diffraction studies of SiOx films with different silicon contents have shown that, upon PPA annealing, arrays of silicon nanocrystals of significantly different average sizes are formed. Moreover, according to the Raman spectroscopy data, PPA does not lead to complete ordering of the structural network of silicon atoms, and some of the atoms, apparently located in small clusters of ~1 nm, retain deviations from interatomic distances and bond angles.

A Macro-Pulse Photon Counting Lidar for Long-Range High-Speed Moving Target Detection

A macro-pulse photon counting Lidar is described in this paper, which was designed to implement long-range and high-speed moving target detection. The ToF extraction method for the macro-pulse photon counting Lidar system is proposed. The performance of the macro pulse method and the traditional pulse accumulation method were compared in theory and simulation experiments. The results showed that the performance of the macro-pulse method was obviously better than that of the pulse accumulation method. At the same time, a laboratory verification platform for long range and high-speed moving targets was built. The experimental results were highly consistent with the theoretical and simulation results. This proved that the macro pulse photon counting Lidar is an effective method to measure long range high-speed moving targets.

Determination of the contributions of degenerate and non-degenerate two-photon absorption response in silicon avalanche photodiode for infrared photon detection

The study of non-linear interactions in semiconductor photo-electronic devices to achieve effective and fast photon identification is an ongoing and important task. We investigated the specific contribution of degenerate and non-degenerate two-photon absorption (D-TPA and ND-TPA) response in silicon avalanche photodiode (Si-APD) for infrared photon detection at room temperature. We experimentally demonstrated that when the two laser pulses overlapped, the average D-TPA quantum detection efficiencies at 1800 nm, and that at 1550 nm were measured as 3.3×10 -16 counts•pulse/photon 2 , 4.3×10 -15 counts•pulse/photon 2 , respectively. And the ND-TPA quantum detection efficiency of 1800 nm and 1550 nm was measured to be 7.9×10 -16 counts•pulse/photon 2 . This study provides a solution for the practical infrared photon detection devices based on TPA effect in Si-APDs.